Thread: 355 combo evaluation -dyno? Thoughts, suggestions, comments appreciated

Tweet

Background: The engine described below is in process. Short block assembled and ready to degree cam. All parts listed purchased. Will need to purchase pushrods after getting mid-lift measurement. Also need converter. I know this build is slightly overbore for a wheeler but I believe this engine should match the power output as my current 250hp tired 350 engine does off idle. Hoping to get feedback and a virtual dyno graph to aid in my decision on torque converter.


Rig:
5000lb 4x4, 1 ton CJ7 Jeep 5.13 gears with 37” tires. TH350 tbd stall converter. Not daily driver. 30% high elevation 5000+ft snow, 30% woods 3-5000 ft, 20% town, 20% coast dunes. Not a rock crawler!

Build: ZZ430 clone(ish) with Lunati hyd roller cam
GM 355 aluminum head, flat top piston. 10.48 static compression, .041” squish. 8.29 Dynamic compression at 1500 ft.

Fitech Go EFI self learning TBI fuel injection (250-600hp) 4barrel
Intake: GM Vortec 12464340 (seprated dual plane, no bleed over cutout)
Phenolic Spacer 4 hole 1"
MSD6AL, MSD 85551 dist, 19 degrees mechanical 34 total. w/ 8561 melonized gear, Blaster coil, Taylor 8mm wires, NGK BKR5EGP plugs @ .050”

Top end:
Original ZZ430 Fastburn aluminum heads 62cc chamber, 2.00/1.55” valves 210/78cc runners. Chamber, bowl, port blend and gasket match to MS 98000. 7/16" studs, Isky adj guideplates, PAC Beehive 1218 springs 130/307lb, 1.80/1.24" install height, .100" coil bind clearance (+.05" locks, .06" retainers), Teflon seals, Scorpion 1003 1.6" roller rockers. Cometic C5245-036 MLS head gaskets 4.06" x .036"

Bump stick: Hyd roller
Lunati Voodoo 270/278 pn: 20120711 (60111)
Adv: 270/278
.05": 219/227
LAS/ICL: 112/106
Overlap 50
Lift: .550/.565 (with 1.6 rockers)
Spring pressure: 130lbs seat 302/307 int/ex open

Comp cam 853-16 retro hyd roller lifters

Block:
SBC 1975 3970010 4 bolt 4.030" bore, line honed .005" deck, cast .010/.010 crank (3.48" stroke) chamfered & balanced, 5.7 Scat rods, L2256 TRW forged 6.1cc 4 valve relief pistons balanced. R-9903 Sealed Power rings (plasma moly top ring), Clevite77 rod/main bearings, ACL 910-3349 cam bearings. Cloyes chain with Torrington bearing and button. Alum water pump. 5 qt cheater pan with tray, std melling pump. Other: .04" oil hole in oil plug for timming chain lubrication, oil return screen kit, ARP main studs, teflon rear seal.

Exhaust:
1 5/8” fenderwell headers (maybe 30”) 3” collector, 2 ½” exhaust with hooker aeromax mufflers total 4’ exhaust each side.

Curios what peramters I should set the fuel injection to control vacuum advance. No can on dizzy. Also, I have the option to lock out the dist mech adv. and use the FI to control also.

Looks like a great build to me. 5.13 with 37" tire will be the same relationship as 3.54 with a 26" tire. I might have gone with 5.38 gears, but you're close.

I would not have used 1.6 rockers in anything but a race motor build, where routine maintenance is practiced. In my opinion, the valvetrain already has enough strain on it without the added strain of higher ratio rockers, particularly with aftermarket springs. They're probably worth only about 10-12 horsepower over 1.5's anyway. I'd use 'em only if I needed extra power to drive around a competitor in structured class racing.

Cam appears to be a very good match and the 112 LSA should help produce sufficient vacuum for power brakes. it should begin making power somewhere around 2000, so a 10", 2500/2800 stall converter might be my choice. Choose a small 10" diameter unit that is designed from the git-go for the purpose, rather than a 12" unit with the fins bent over.

Squish/quench is right on the money at 0.041".

Install an H pipe immediately after the collectors for better sound and a slight increase in power. The motor will like a good balance side to side.

Sorry, I know nothing at all about EFI, but maybe one of the other fellows on the board will chip in.

Some pics would be appreciated.
.

Tech-I wish you'd take the time some day to reconsider the 1.6 rockers on the sbc-there are a few reasons that they are a good/decent choice--------with so many engines ending up getting small base circle cams to clear the rods on the sbc, the profiles of the cam lobe do get some serious restrictions---------its difficult to get the higher lifts at the valves with even the 1.6 rockers vs the 1.5 but they really don't add as much strain to the train ( poem?) as might be thought because the long part of the arm only sees what comes from the valve/spring combo and the short side the additional leverage needed to multiple .1 more force. There ar rasons practically every engine uses the 1.73, 1.75 ratios and these days even up to the 2.2 area-------makes the cam lobes more lemon shaped compared to egg-------

Techinspector:
Thank you for the feedback. I have thought about trading my 1.6 Scorpion rockers for some 1.5's just to simmer down the wear on valve train components. Maybe someone here has an interest to trade. I just dont want to trade new for used. In the past few years of the gathering of parts and such I have read a bit on the wear aspect (after I bought them of corse...). Prior I was all about the free horsepower.

You are spot on for torque converter selection as my research from Coan, Yank and TCI. Ok, here is my dillema. One of the use conditions in my rig is downhill slow speed. I have been in situations were braking is not really ideal. Rather idle down in gear. My fear is that a converter more than a few hundred RPM over stock will suck. In addition some obsticles up hill would be best navigated with the same type of low stall converter. My thought is that if the dyno numbers are close enough to make power at the lower rpm I could sacrifice the ideal stall speed for a lower stall.

DO you think this engine would make reasonable power down low to justify the lower stall. Note I have the th350 built with a Transgo kit to hold 1st and 2nd while full auto in 3rd.

Jerry Clayton:
You bring up an interesting point. In fact, the fastburn heads came with self aligning 1.6 roller rockers (I think crane made for GM with the bowtie logo). Side note: during mock up of the self aligning jobbers I noticed two of the pushrods were touching the intake runner. Kinda screwy design if you ask me. I went with the big tip scorpions and adjustable guideplates to get the pushrod off the intake runner and keep the valve tip fully contacted with the larger roller tip hanging off one side.

Maybe the thought is the added lift with the inceased ratio rocker does not equate to a substantial amount of added wear. WTF is substantial!
For my application 1.6 rockers equaling .565 lift using the ideal midlift set up calculates to .029" scrub or pattern on the valve tip.
1.5 rockers equaling .530" lift reduces the scrub to .026"
.003" difference is 10% added pattern.

.003" delta or 10% increase seems small but what is the added stress on the valve guide? Beats me... if using behives they claim an increased center hold by design. Seems reasonable to say Behive springs would reduce the wear of the valve guides.

I have no idea what this translates to pushrod to rocker cup wear.

Very interesting point.

I hear a lot about people saying their rig is sluggish due to a low stall. For those that experience this with a similar combo as mine, is it a serious issue or is it that you wanted the rig to jump like a whipped quarter horse? I am trying to justify a lower stall than optimal to balance drive ability.

Originally Posted by techinspector1

Some pics would be appreciated.
.

Took 2 degrees advance to get it dialed in to the cam card at 106...
https://imgur.com/5o6rE83